1. Field of the Invention
The present invention relates to a toroidal type continuously variable transmission which can be utilized as a transmission for an automobile and other machines.
2. Related Background Art
A toroidal type continuously variable transmission as shown in FIGS. 2A and 2B has been investigated as a transmission for an automobile. This toroidal type continuously variable transmission has an input side disk 2 supported concentrically with an input shaft 1 and an output side disk 4 fixed to an end portion of an output shaft 3, as disclosed, for example, in Japanese Laid-Open Utility Model Application No. 62-71465. On the inner surface of a casing which accommodates the toroidal type continuously variable transmission or on a supporting bracket disposed in this casing, there are provide trunnions 5 which swing about pivots 16 located at twisted positions with respect to the input shaft 1 and the output shaft 3, respectively.
Each of the trunnions 5 is made of a metal material having a sufficient rigidity and provided with the pivots 16 mounted on the outer surface of both ends. Also, around displacement shafts 6, each disposed in a central portion of each trunnion 5, power rollers 7 are rotatably supported. Each of the power rollers 7 is sandwiched between the input side and output side disks 2, 4.
The side surfaces in the axial direction of the input side and output side disks 2, 4, opposite to each other, are formed with an input side concave surface 2a and an output side concave surface 4a, respectively, the cross-section of which is arcuate with the center being on the corresponding pivots 16. Then, the outer peripheral faces 7a of the respective power rollers 7 formed in spherical convex surfaces abut the input side concave surface 2a and the output side concave surface 4a of the disks 2, 4, respectively.
Between the input shaft 1 and the input side disk 2, there is provided a loading cam type pressurizing unit 8 with which the input side disk 2 is resiliently urged to the output side disk 4. This pressurizing unit 8 comprises a cam plate 9 arranged for rotation together with the input shaft 1 and a plurality of (for example, four) rollers 11 retained by a retainer 10. On one side face of the cam plate 9 (the right side face in FIG. 2), there is formed a cam plane 12 which presents unevenness in the circumferential direction. A similar cam plane 13 is also formed on the outer side face (the left side face in FIG. 2) of the input side disk 2. The plurality of rollers 11 are arranged rotatably about an axis in the radial direction with respect to the center of the input shaft 1.
When rotation of the input shaft 1 causes the cam plate 9 to rotate, the plurality of rollers 11 are urged onto the cam plane 13 on the outer side face of the input side disk 2. As a result, the input side disk 2 is urged by the plurality of power rollers 7, and simultaneously the input side disk 2 is rotated on the basis of the engagement of the pair of cam planes 12, 13 with the plurality of rollers 11. Then, the rotation of the input side disk 2 is transmitted to the output side disk 4 through the plurality of power rollers 7, which causes rotation of the output shaft 3 fixed to the output side disk 4.
Outer rings 14 are mounted to base end portions of the respective displacement shafts 6 such that a plurality of rolling bodies 17 (normally balls. See FIG. 1 showing an embodiment of the present invention) are retained in annular retainers 15 disposed between the outer rings 14 and the power rollers 7 such that they can freely roll, allowing each of the power rollers 17 to be rotatable relative to the corresponding outer ring 14. Also, though not shown, a plurality of rolling bodies (normally needles) are provided also between the outer peripheral face of each of the displacement shafts 6 and the inner peripheral face of each of the power rollers 7 to arrange the respective power rollers 7 for rotation relative to the corresponding displacement shafts 6.
Consider now that the rotational speed between the input shaft 1 and the output shaft 3 is changed. First, when the speed between the input shaft 1 and the output shaft 3 is decreased, the respective trunnions 5 are swung about the pivots 16 as shown in FIG. 2A to incline the respective displacement shafts 6 such that the outer peripheral faces 7a of the respective power rollers 7 abut a portion near the center of the input side concave surface 2a and a portion near the outer periphery of output side concave surface 4a, respectively.
Conversely, when the speed is increased, the trunnions 5 are swung as shown in FIG. 2B to incline the respective displacement shafts 8 such that the outer peripheral faces 7a of the respective power rollers 7 abut a portion near the outer periphery of the input side concave surface 2a and a portion near the center of the output side concave surface 4a, respectively. If the inclination angle of the displacement shafts 6 is adjusted to be an intermediate value between those shown in FIGS. 2A and 2B, an intermediate transmission gear ratio can be achieved between the input shaft 1 and the output shaft 3.
For the toroidal type continuously variable transmission constructed and operated as described above to exhibit a desired transmission performance, the input side concave surface 2a, the output side concave surface 4a, and the outer peripheral faces 7a of the respective power rollers 7 must be formed in spherical surfaces as desired in order to ensure that power is transmitted between contacted surfaces. However, with the power rollers 7 incorporated in conventional toroidal type continuously variable transmission, positioning of the outer peripheral faces 7a is extremely difficult when they are subjected to a grinding process. It is therefore difficult to finish the outer peripheral faces 7a to have exact spherical convex surfaces by utilizing industrial mass-production techniques.
Also, in operation of the toroidal type continuously variable transmission, the displacement shafts 6 may suffer from elastic deformation so that the power rollers 7 supported by end portions of the respective displacement shafts 6 and the outer rings 14 are inevitably displaced to the direction perpendicular to the respective displacement shafts 6. In this event, it is necessary to prevent the outer peripheral faces of the respective outer rings 14 from coming in contact with the input side concave surface 2a and the output side surface 4a to protect the respective concave surfaces 2a, 4a from being damaged, from a viewpoint of ensuring the durability of the toroidal type continuously variable transmission.
However, the conventionally proposed toroidal type continuously variable transmissions have been manufactured without the consideration of the above stated problems. Therefore, if the respective displacement shafts 6 are elastically deformed in a condition that the displacement shafts 6 are largely inclined, and the outer peripheral faces of the respective outer rings 14 are opposed to the input side concave surface 2a or the outer side concave surface 4a, as shown in FIGS. 2A and 2B, the outer peripheral edges of the respective outer rings 14 rub against the input side concave surface 2a or the output side concave surface 4a, which may result in that the respective concave surfaces 2a, 4a are damaged.
Further, the outer peripheral faces 7a of the power rollers 7 are made in a spherical convex surface so that they are allowed to contact the respective concave surfaces 2a, 4a. For forming such a spherical convex surface using a processing machine such as a grinding machine, it is necessary, to hold the power rollers 7 on a holder of a shoe type. For this reason, in the past, the outer peripheral face 7a of the power roller 7 has been formed of a spherical surface portion 37 and a cylindrical surface portion 38, as shown in FIG. 4. The center of the spherical surface portion 37 is located on the center line of the pivot 16, while the center of the cylindrical surface portion 38 is made coincident with the center of the displacement shaft 6. When the spherical surface portion 37 is processed, the cylindrical surface portion 38 must be held by a holder of a processing machine.
One toroidal type continuously variable transmission of the present invention achieves a reduction of a risk that corner portions of the power rollers 7 come in contact with the input side concave surface 2a or the output side concave surface 4a to improve the durability thereof.
Assume that the spherical surface portion 37 and the cylindrical surface portion 38 continuous from one end of the spherical surface portion 37 are formed on the outer peripheral face 7a of the power roller 7, as the conventional structure shown in FIG. 4. With the same size of the power roller, it is inevitable that the length 1 of the bus line of the spherical surface portion 37 becomes shorter than that without the cylindrical surface portion 38.
In operation of the toroidal type continuously variable transmission, the spherical surface portion 37 comes in contact with the input side concave surface 2a and the output side concave surface 4a in an elliptic portion (contact ellipse), the major axis of which extends in the direction of the bus line of the spherical surface portion 37. In a normal operating state, the major axis of the contact ellipse is short so that the contact ellipse will not extend beyond the spherical surface portion 37. However, if a torque transmitted by the toroidal type continuously variable transmission becomes excessive by some reason, it can be thought that one end portion in the major axis direction of the contact ellipse extends beyond the spherical surface portion 37.
If the contact ellipse extends beyond the spherical surface portion 37, an edge 39 existing in a boundary between the spherical surface portion 37 and the cylindrical surface portion 38 comes in contact with the input side concave surface 2a and the output side concave surface 4a. In this manner, if the sharp edge 39 is in contact with the respective concave surfaces 2a, 4a, parts of the respective concave surfaces 2a, 4a are applied with excessive stresses, resulting in a risk that the concave surfaces 2a, 4a are damaged by the sharp edge 39.
FIGS. 11 and 12 shows an example of toroidal type continuously variable transmissions which are actually used as a transmission for automobile or the like. The structure shown in FIGS. 11, 12 includes two sets of the toroidal type continuously variable transmissions having a basic structure as shown in FIGS. 2A and 2B which are arranged in parallel with each other. This is because as much power as possible can be transmitted as a whole, while one of the two toroidal type continuously variable transmission sets is prevented from being applied with an excessive load.
Referring in detail to FIGS. 11, 12, trunnions 106 are supported by a supporting member 107. This supporting member 107 is constructed of a lower link 116, two upper links 117, and an upper link post 118, which are combined with one another. Inside of circular holes 119, 120 formed through four corner portions of the lower link 116 and through both end portions of the upper links 117, respective pivots 105 arranged in both ends of the trunnions 106 are pivotably supported through roller bearings 121.
Also, inside of circular holes 122 formed in an intermediate portions of the respective trunnions 106, respective base ends of displacement shafts 108 are rotatably supported through radial bearings 123. Further, each of the power rollers 109 is rotatably supported by the top end of each of the displacement shafts 108 through another radial bearing 124. A pair of thrust bearings 125 are disposed between opposing side surfaces 106a of the trunnions 106 and end surfaces 109b of the power rollers 109, so that thrust loads applied to the respective power rollers 109 can be supported by the respective trunnions 106.
Each of the thrust bearings 125 is constructed of an outer ring 131, a plurality of balls 126, and a retainer 127 for retaining the plurality of balls 126 such that these balls 126 can freely roll. The outer surface of the outer ring 131 abuts the side surfaces 106a of the trunnions 106 through a thrust needle bearing 128, while the plurality of balls 126 are held between an outer annular trajectory formed in the inner surface of the outer ring 131 and an inner annular trajectory formed in the end surfaces 109b of the power rollers 109.
The retainer 127 is implemented by a so-called machined retainer made of a metal plate of a material such as HBsCl (high tension brass) which is formed in a ring shape as shown in detail in FIGS. 9, 10, and provided with a plurality of circular pockets 129 at equally spaced positions in the circumferential direction of the metal plate. The inner diameter of an opening at one end (the lower end in FIG. 10) of each pocket 129 is made shorter than the outer diameter of the balls 126 and the inner diameter of an opening at the other end (the upper end in FIG. 10) thereof. 0n the inner surface of the opening at the one end, there is formed a curved portion 130 in conformity to the outer diameter of the ball 126.
When each ball 126 is to be retained in each pocket 129, the ball 126 is inserted into the pocket 129 from the opening at the other end, and then caulking is performed for reducing the inner diameter of the opening at the other end by pressing a punch at a position indicated by the solid line a in FIG. 9. As a result, the diameters of the openings at both ends of each pocket 129 is shorter than the outer diameter of the ball 126, so that the ball 126 will not drop from the pocket 129.
Another toroidal type continuously variable transmission of the present invention improves the thrust bearings 125 for supporting thrust loads applied to the respective power rollers 109 to achieve reduction in weight and improvement in performance of the transmission.
Since each of the thrust bearings 125 in the conventional structure as described above has the metal retainer 127 incorporated therein, it implies problems that not only the weight is extremely heavy, but also assembly thereof is complicated, e.g., because of the caulking required to prevent the balls 126 from dropping from the respective pockets 129, which results in a raised manufacturing cost.
Further, for taking a caulking margin, a wide space, to some degree, must be ensured between adjacent two pockets 129. Therefore, if the diameters of the balls 126 are assumed to be equal, the number of the pockets 129 and the balls 126 are reduced due to such spaces for the caulking. For providing the same number of balls, the diameter of the balls 126 must be reduced in correspondence to the caulking margins. As the number of the balls 126 is reduced or as the diameter of the same is shorter, a load capacity of each thrust bearing 125 is decreased, resulting in reducing a torque which can be transmitted by a toroidal type continuously variable transmission having the thrust bearings 125 incorporated therein.
Particularly, when the retainer 127 is made of a metal, a slight gap is required between the inner surface of each pocket 129 and the outer surface of the ball 126 accommodated therein. For this reason, the rotation of the balls 126 is guided by a so-called trajectory wheel guiding which is based on the trajectory along which the balls 126 are rolling in contact therewith.
In operation of the toroidal type continuously variable transmission, each of the power rollers 109 receives large loads at two circumferential points by an input side disk 102 and an output side disk 104. As a result, loads applied to each of the thrust bearings 125 become unequal over the circumferential direction. Thus, each of the trunnions 106 is elastically deformed by a large load received from the corresponding power roller 109, whereby the shape of the trajectory is also deformed slightly from a true circle to an ellipse.
If the balls 126 rotate together with the retainer 127 while the trajectory remains deformed in an elliptical shape, the balls loosely retained in the pockets 129 roll along the elliptically deformed trajectory. In other words, a so-called whirling phenomenon occurs. Such a whirling phenomenon, if occurs, may easily cause the trajectory to be unequally rubbed and noise and vibration to be generated during operation.